1. Field of the Invention
This invention relates to apparatus and methods for threshold comparison and in particular, but not exclusively, to such apparatus and methods which use opto-electronic techniques for effecting weightless neural threshold comparison.
2. Discussion of Prior Art
There is a wide range of applications where it is required to effect a threshold comparison of a weightless binary string. A weightless binary string is one in which the bit position of the logic 1""s and 0""s is immaterial; thus in weightless binary {00101101} has the same weightless value as {10110100} because the number of 1""s set in each is the same. Weightless binary numbers are a set of binary digits 1 and 0, each representing just xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d respectively. There is no least significant bit (LSB) or most significant bit (MSB). The set of bits may be ordered or without order. For example this determination may be used in a binary neuron, or for optical devices implementing the arrangements described in our co-pending published International Application Nos. W099/33019 and W099/33175 the entire contents of which are incorporated herein by reference.
This type of comparison may be required in flight control systems, voting systems with redundancy, safety critical systems, telecommunications systems, decision making systems, and artificial intelligence systems, such as neural networks.
In a prior art arrangement, a state machine based system may be used to count the number of 0""s and 1""s set, and digital arithmetic units used for the comparison. For each binary string, each bit is scanned sequentially and a counter or arithmetic register incremented accordingly. Thereafter the contents of the respective counters or arithmetic registers may be compared to determine the relationship between the number of 0""s and 1""s set. This type of arrangement may be implemented in software using a microprocessor or a similar state machine.
However this technique is slow and prone to both conductive and emissive radio frequency interference (RFI) as it relies principally on clocks, counters and microprocessors. Both the speed of operation and susceptibility to is disruption or corruption by other noise makes such a system ill-suited for safety critical systems such as flight control systems.
Accordingly we have provided an arrangement for determining the relationship between the number of 0""s and 1""s set in a binary string, which does not require a counter or register and does not require a microprocessor or the like for implementation.
Accordingly, in one aspect this invention provides a comparator for receiving a string of binary bits and for comparing the bits to determine the relative quantities of logic 0""s and 1""s, said comparator including:
a plurality of energy emitting transducer elements each for receiving a respective bit of said string, and each for outputting energy of a first characteristic on receiving a logic xe2x80x9c0xe2x80x9d and for outputting energy of a second characteristic on receiving a logic xe2x80x9c1xe2x80x9d, and
output means for observing the energy emitted from said plurality of transducers and for outputting a respective output signal indicating whether the number of logic 0""s is greater than or less than the number of logic 1""s.
By this arrangement the relationship between the number of 0""s and 1""s set is determined by observation of the energy in each of the first and second characteristics.
Preferably, the comparator is operable further to indicate if the number of logic 0""s is equal to the number of logic 1""s.
The energy may be provided by any suitable transducers, which are capable of emitting distinguishable radiation and which are reasonably free from significant interference from external sources.
Preferably, said energy emitting transducer elements comprise radiation emitting transducer elements emitting radiation of different characteristics. Thus they may emit light in two different wavebands according to the applied input. They may emit light of different polarisations.
However the invention also extends to arrangements which incorporate LED""s Laser Diodes, IR LED""S, UV LED""s, filament bulbs, CRTs, sound and ultrasonic emitters, microwaves, etc.
Preferably, said transducer elements comprise light emitting diodes. The light emitting diodes may be bi- or tri-color light emitting diodes.
Preferably, the transducer elements are disposed in a regular array.
Preferably, said output means comprises respective first and second sensor means responsive to the radiation in said first and second wavebands to output respective output signals indicative of the relative intensities thereof. For example, the first and second sensor means may include first and second filter means respectively, for selectively passing the respective waveband to be detected.
Preferably said output means further includes means for comparing the output signals from the first and second sensor means to determine whether the number of logic 0""s supplied to said transducer elements is greater than or less than the number of logic 1""s supplied thereto.
In another aspect, this invention provides a method of comparing the bits in a binary string to determine the relative quantities of logic 0""s and logic 1""s, which comprises applying said bits to respective transducer elements which output radiation of a first characteristic if a logic 0 is applied and output radiation of a second characteristic if a logic 1 is applied, and monitoring the relative intensities of the respective energies.
In another aspect, this invention provides a comparator for receiving a string of binary bits and for comparing the bits to determine the relative quantities of logic 0""s and 1""s, said comparator including:
a plurality of energy emitting transducer elements adapted to be responsive to binary bits in said string and the plurality being capable of emitting energy of two different characteristics, wherein the number of logic xe2x80x980xe2x80x99 bits in the string causes a corresponding number of transducer elements to emit energy of one of said characteristics, and the number of logic xe2x80x981xe2x80x99 bits cause a corresponding number of the transducer elements to emit energy of the other of said characteristics.
Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description.